This invention relates to the field of intravascular medical devices, and more particularly, to intravascular catheters that use a relatively stiff proximal section and a more flexible distal section for improved pushability, trackability and crossability.
Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). These therapeutic techniques are well known in the art and typically involve the use of a balloon catheter with a guide wire, possibly in combination with other intravascular devices. A typical balloon catheter has an elongate shaft with a balloon attached proximate the distal end and a manifold attached to the proximal end. In use, the balloon catheter is advanced over the guide wire such that the balloon is positioned adjacent a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
There are three basic types of intravascular catheters for use in such procedures including fixed-wire catheters, over-the-wire (OTW) catheters and single-operator-exchange (SOE) catheters. The general construction and use of FW, OTW and SOE catheters are all well known in the art.
Several characteristics that are important in intravascular catheters include pushability, trackability and crossability. Pushability refers to the ability to transmit force from the proximal end of the catheter to the distal end of the catheter. Trackability refers to the ability to navigate tortuous vasculature. Finally, crossability refers to the ability to navigate the balloon catheter across narrow restrictions in the vasculature.
To maximize pushability, some prior art catheters incorporate a stainless steel outer tube (also referred to as a hypotube) on the proximal shaft section and a polymeric distal shaft section. One limitation of such a construction is that hypotubing is often prone to kinking. To reduce the likelihood of kinking, some prior art catheters use a relatively stiff polymer (e.g., composite) or reinforced polymer in the proximal shaft section.
The trackability of a particular catheter design is analyzed in terms of the trackability of the distal portion of the catheter, as this portion must track the guidewire through small tortuous vessels to reach the stenosed area to be treated. A more flexible distal portion has been found to improve trackability. Therefore, to maximize pushability, the catheter should have a relatively stiff proximal section. To maximize trackability, the catheter should have a relatively flexible distal section.
A limitation of this basic structure is that kinking can occur at the joint between the relatively stiff proximal shaft section and the relatively flexible distal shaft section. To reduce the likelihood of kinking, some prior art catheters use one or more tubular sections of intermediate flexibility between the relatively stiff proximal section and the relatively flexible distal section to provide a more gradual transition in flexibility therebetween. While this approach provides some benefit, the resulting transition in flexibility is often step wise, and can still be susceptible to kinking at the junctions of the various intermediate sections. It would be desirable, therefore, to provide an intravascular catheter that has a more gradual transition in flexibility along its length.
The present invention overcomes many of the disadvantages of the prior art by providing a transition member that transitions or varies the stiffness of a catheter from a stiffer more pushable proximal section to a more flexible and trackable distal section, while reducing kinkability in the transition. The transition member preferably has a spiral cut provided therein over at least a portion of its axial length to increase the flexibility of the transition member. The pitch of the spiral cut is varied to facilitate a gradual transition in flexibility along the catheter as supported by the transition member. It is contemplated that the transition member may be used in conjunction with all types of catheters including, but not limited to, single-operator-exchange type catheters, over-the wire type catheters, and/or fixed-wire type catheters.
In one illustrative embodiment of the present invention, the transition member is used in conjunction with a catheter or other device that has a relatively stiff proximal section and a relatively flexible distal section. The junction between the stiffer proximal section and the more flexible distal section provides a transition in flexibility along the length of the catheter. Preferably, the transition member is co-axially disposed relative to the catheter shaft or other device, and is longitudinally positioned to bridge, extend across, or overlap at least part of the junction of the stiffer proximal section and the relatively flexible distal section. In a preferred embodiment, the transition member is included on a catheter having an outer tubular member which has a proximal stiff segment and a distal more flexible segment with the transition member extending both distally and proximally from the junction between these members. In a preferred over-the-wire catheter, an inner tubular member extends coaxially with the lumen of the outer tubular member and the transition member is affixed to the inner tubular member at an axial location proximate the junction in outer segments.
The flexibility of the transition member preferably increases along its length. This can be accomplished by providing a spiral cut or the like which extends through the side wall of the transition member. The spiral cut provides flexibility to the transition member, and if the pitch of the spiral cut is changed over the length, can provide a relatively smooth transition in flexibility from the relatively stiff proximal section to the relatively flexible distal section of the catheter while providing increased kink resistance. The transition member may be made from a stainless steel hypotube or other metallic tube, such as nitinol, an un-reinforced polymeric tube, a reinforced polymeric tube, or any other suitable material or element.
The transition member preferably has a first end region, an intermediate region, and a second end region, wherein only the first end region is secured to the catheter shaft. The intermediate region and the second end region are preferably left floating relative to the catheter shaft. In a preferred embodiment, the intermediate region and/or the second end region are radially spaced from the shaft when the catheter is in a substantially straight configuration, and are in engagement with at least part of the catheter shaft when the catheter is in a bent configuration.
The first end region of the transition member is secured to the shaft proximate the transition of flexibility of the shaft, with the intermediate region and the second end region extending distally therefrom. The length of the transition member is preferably sufficient so that the second end region is distal of the transition in flexibility of the shaft. Thus, like above, the transition member may bridge, extend across, or overlap least part of the transition in flexibility of the catheter shaft.
As previously stated, in preferred embodiments, the transition member is part of or affixed to a co-axial type catheter that includes an elongate outer tube having a transition in flexibility and an elongate inner member. In one embodiment, the inner member is coaxially disposed within the lumen of the outer tube to form an annular lumen therebetween. The transition member is then preferably affixed to the inner member so that it extends coaxially therewith. The transition member extends axially from a point at or proximal of the transition in flexibility of the outer tube to a point at or distal of the transition in flexibility of the outer tube. It is contemplated that the inner member may be a inner tubular member having a guide wire lumen extending therethrough. Alternatively, it is contemplated that the inner member may be a guide wire or any other suitable device or structure. It is further recognized that the inner member can include a transition in flexibility. The transition member can be mounted on the inner member, or affixed to the outer member at an axial position so that the transition member proximal end is at or proximal to the transition flexibility and the distal end is at or distal of the transition in flexibility to provide kink resistance for the inner tubular member.
Preferably, the transition member is co-axially disposed within the annular lumen between the inner member and outer tube. It is recognized, however, that the transition member may be positioned inside the inner member (if the inner member is tubular having an inner lumen) or outside of the outer tube. The transition member is preferably positioned adjacent to at least a portion of the transition in flexibility of the catheter shaft, and is spiral cut along its length. Also, the pitch of the spiral cut may be varied at a constant or variable rate, depending on the desired flexibility characteristics of the transition member.
The outer tube may have a proximal outer section and a distal outer section joined together at a junction, with the distal outer section more flexible than the proximal outer section. The proximal end of the transition member is preferably located proximal of the junction and the distal end is preferably located distal of the junction. That is, the transition member preferably spans or bridges at least part of the transition in flexibility (i.e., junction) of the outer tube.
As previously stated, the inner member may also have a transition in flexibility. In one embodiment, the inner member has a proximal portion, an intermediate portion, and a distal portion, wherein the proximal portion has a first outer diameter, the distal portion has a second outer diameter that is smaller than the first outer diameter, and the intermediate portion has an outer diameter that tapers from the first outer diameter to the second outer diameter. The tapered intermediate portion corresponds to the transition in flexibility of the inner member.
In a preferred embodiment, the transition member is secured to or proximate to the intermediate portion of the inner member and extends distally therefrom. To help secure the transition member to the inner member, the transition member may have a proximal portion sized so that the transition member can be friction fit over a portion of the tapered portion of the inner tube. An adhesive may also be used to secure the transition member to the intermediate portion of the inner tube. In a preferred embodiment adhesive is applied proximate the proximal end of the transition member only so that the transition member distal of the adhesive is free-floating. As discussed above, the transition member may engage at least part of the inner member and outer tube when the catheter is provided in a bent configuration.